/*
 * Copyright 2013 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.util;

import io.netty.util.internal.StringUtil;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;

/**
 * Collection of method to handle objects that may implement
 * {@link ReferenceCounted}.
 */
public final class ReferenceCountUtil
{

    private static final InternalLogger logger = InternalLoggerFactory
            .getInstance(ReferenceCountUtil.class);

    /**
     * Try to call {@link ReferenceCounted#retain()} if the specified message
     * implements {@link ReferenceCounted}. If the specified message doesn't
     * implement {@link ReferenceCounted}, this method does nothing.
     */
    @SuppressWarnings("unchecked")
    public static <T> T retain(T msg)
    {
        if (msg instanceof ReferenceCounted)
        {
            return (T) ((ReferenceCounted) msg).retain();
        }
        return msg;
    }

    /**
     * Try to call {@link ReferenceCounted#retain(int)} if the specified message
     * implements {@link ReferenceCounted}. If the specified message doesn't
     * implement {@link ReferenceCounted}, this method does nothing.
     */
    @SuppressWarnings("unchecked")
    public static <T> T retain(T msg, int increment)
    {
        if (msg instanceof ReferenceCounted)
        {
            return (T) ((ReferenceCounted) msg).retain(increment);
        }
        return msg;
    }

    /**
     * Tries to call {@link ReferenceCounted#touch()} if the specified message
     * implements {@link ReferenceCounted}. If the specified message doesn't
     * implement {@link ReferenceCounted}, this method does nothing.
     */
    @SuppressWarnings("unchecked")
    public static <T> T touch(T msg)
    {
        if (msg instanceof ReferenceCounted)
        {
            return (T) ((ReferenceCounted) msg).touch();
        }
        return msg;
    }

    /**
     * Tries to call {@link ReferenceCounted#touch(Object)} if the specified
     * message implements {@link ReferenceCounted}. If the specified message
     * doesn't implement {@link ReferenceCounted}, this method does nothing.
     */
    @SuppressWarnings("unchecked")
    public static <T> T touch(T msg, Object hint)
    {
        if (msg instanceof ReferenceCounted)
        {
            return (T) ((ReferenceCounted) msg).touch(hint);
        }
        return msg;
    }

    /**
     * Try to call {@link ReferenceCounted#release()} if the specified message
     * implements {@link ReferenceCounted}. If the specified message doesn't
     * implement {@link ReferenceCounted}, this method does nothing.
     */
    public static boolean release(Object msg)
    {
        if (msg instanceof ReferenceCounted)
        {
            return ((ReferenceCounted) msg).release();
        }
        return false;
    }

    /**
     * Try to call {@link ReferenceCounted#release(int)} if the specified
     * message implements {@link ReferenceCounted}. If the specified message
     * doesn't implement {@link ReferenceCounted}, this method does nothing.
     */
    public static boolean release(Object msg, int decrement)
    {
        if (msg instanceof ReferenceCounted)
        {
            return ((ReferenceCounted) msg).release(decrement);
        }
        return false;
    }

    /**
     * Try to call {@link ReferenceCounted#release()} if the specified message
     * implements {@link ReferenceCounted}. If the specified message doesn't
     * implement {@link ReferenceCounted}, this method does nothing. Unlike
     * {@link #release(Object)} this method catches an exception raised by
     * {@link ReferenceCounted#release()} and logs it, rather than rethrowing it
     * to the caller. It is usually recommended to use {@link #release(Object)}
     * instead, unless you absolutely need to swallow an exception.
     */
    public static void safeRelease(Object msg)
    {
        try
        {
            release(msg);
        }
        catch (Throwable t)
        {
            logger.warn("Failed to release a message: {}", msg, t);
        }
    }

    /**
     * Try to call {@link ReferenceCounted#release(int)} if the specified
     * message implements {@link ReferenceCounted}. If the specified message
     * doesn't implement {@link ReferenceCounted}, this method does nothing.
     * Unlike {@link #release(Object)} this method catches an exception raised
     * by {@link ReferenceCounted#release(int)} and logs it, rather than
     * rethrowing it to the caller. It is usually recommended to use
     * {@link #release(Object, int)} instead, unless you absolutely need to
     * swallow an exception.
     */
    public static void safeRelease(Object msg, int decrement)
    {
        try
        {
            release(msg, decrement);
        }
        catch (Throwable t)
        {
            if (logger.isWarnEnabled())
            {
                logger.warn("Failed to release a message: {} (decrement: {})",
                        msg, decrement, t);
            }
        }
    }

    /**
     * Schedules the specified object to be released when the caller thread
     * terminates. Note that this operation is intended to simplify reference
     * counting of ephemeral objects during unit tests. Do not use it beyond the
     * intended use case.
     *
     * @deprecated this may introduce a lot of memory usage so it is generally
     *             preferable to manually release objects.
     */
    @Deprecated
    public static <T> T releaseLater(T msg)
    {
        return releaseLater(msg, 1);
    }

    /**
     * Schedules the specified object to be released when the caller thread
     * terminates. Note that this operation is intended to simplify reference
     * counting of ephemeral objects during unit tests. Do not use it beyond the
     * intended use case.
     *
     * @deprecated this may introduce a lot of memory usage so it is generally
     *             preferable to manually release objects.
     */
    @Deprecated
    public static <T> T releaseLater(T msg, int decrement)
    {
        if (msg instanceof ReferenceCounted)
        {
            ThreadDeathWatcher.watch(Thread.currentThread(),
                    new ReleasingTask((ReferenceCounted) msg, decrement));
        }
        return msg;
    }

    /**
     * Releases the objects when the thread that called
     * {@link #releaseLater(Object)} has been terminated.
     */
    private static final class ReleasingTask implements Runnable
    {

        private final ReferenceCounted obj;

        private final int decrement;

        ReleasingTask(ReferenceCounted obj, int decrement)
        {
            this.obj = obj;
            this.decrement = decrement;
        }

        @Override
        public void run()
        {
            try
            {
                if (!obj.release(decrement))
                {
                    logger.warn("Non-zero refCnt: {}", this);
                }
                else
                {
                    logger.debug("Released: {}", this);
                }
            }
            catch (Exception ex)
            {
                logger.warn("Failed to release an object: {}", obj, ex);
            }
        }

        @Override
        public String toString()
        {
            return StringUtil.simpleClassName(obj) + ".release(" + decrement
                    + ") refCnt: " + obj.refCnt();
        }
    }

    private ReferenceCountUtil()
    {
    }
}
